Binders which have been commonly used for magnetic recording media include thermoplastic resins such as vinyl chloride-vinyl acetate resins, vinyl chloride-vinylidene chloride resins, cellulose resins, acetal resins, urethane resins and acrylonitrile-butadiene resins used alone or in combination. However, with such binders the magnetic layer generally has poor wear resistance and the tape guiding systems which contact with magnetic tapes are stained during tape running.
Various improvements have been proposed where a thermosetting resin such as melamine resins or urea resins is used as a binder, or a binder which can be cross-linked by a chemical reaction such as in isocyanate compound or an epoxy compound is added to the above-described thermoplastic resins. However, disadvantages occur when using such cross-linking type binder. Firstly, the storage stability of the resin solution in which ferromagnetic particles are dispersed is low, i.e., the pot life is short and the physical properties of the resulting magentic coating composition cannot be kept homogeneous, and accordingly, magnetic tapes cannot be uniformly prepared. Secondly, after coating and drying the magnetic coating composition, heat treatment is necessary to cure a coating layer thereby requiring a long period of time to manufacture magnetic recording media.
In order to eliminate the above disadvantages, a method has been proposed where a magnetic recording medium is prepared by using a combination of an acrylate oligomer and an acrylate type monomer as a binder and curing the binder by electron beam radiation after drying, as disclosed in Japanese Patent Publication No. 12423/72, Japanese Patent Application (OPI) Nos. 13639/72, 15104/72, 77433/75, 25231/81, 86130/82, 86131/82 and 127926/82 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), U.S. Pat. No. 4,368,239, German Pat. No. 2,100,037 and Dutch Pat. No. 7,118,222. However, a magnetic recording medium having satisfactory durability and electromagnetic properties cannot be obtained in accordance with the above-described conventional methods.
Recently, it has been strongly desired that the video head abrasiveness of a video tape recorder (hereinafter "head abrasiveness") be minimized in VHS and .beta.-type home video cassette tape recorders.
Further, as video cassette tape recorders have come to have multi-functions, video tapes used therefor are required to withstand use under severe conditions. However, it has hitherto been impossible to produce a magnetic recording medium having a magnetic layer which is provided with durability and electromagnetic properties as well as less head abrasiveness which satisfy the above requirements.
The inventors have attained the present invention as a result of extensive studies for improvements of conventional magnetic recording media.